| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | had been [verb] | 37993 |
|
| 2 | had been [v-ing] | 5819 |
|
| 3 | [verb] been operating | 92 |
|
| 4 | have been operating | 92 |
|
| 5 | had been operate | 33 |
|
| 6 | [vb past] been operating | 19 |
|
| 7 | had [been] operating | 19 |
|
| 8 | had [be] operating | 19 |
|
| 9 | had be operating | 19 |
|
